I would worry about the future, though. I'm skeptical that updating to
GTK 4 will ever be possible (due to the removal of the foreign drawing
API that allows non-GTK apps to render boxes and buttons and such using
the GTK theme). So even if it's the best option today, I don't see much
long-term future here. I'm not sure what the Java community should be
doing, but probably thinking about this early would be better than
waiting until GTK 4 is released and it's too late for major changes.
Slight correction: with GTK4 it's still possible to create render nodes and use them to render CSS state, but you have to handle that state on your own. In practice, this means you won't be able to use GTK API to render stuff that looks like a GTK widget according to the current theme; if you want something that looks like a GtkWidget, you need to use GtkWidget.
Ciao,
Emmanuele
